Explore: Time selector, split view, design integration

Fix cache busting for systemjs imports for plugins

[skip ci]

influxdb: support count distinct aggregation

Show create dashboard link if at least editor in one folder

Changed Prometheus interval-alignment to cover whole panel range

[skip ci]

As public/app/plugins/datasource/cloudwatch/partials/config.html and this file differ between the AWS regions available, I've updated the latest so they share the same data.
In that way, the regions() method in dashboards returns the same list as the frontend does.

graphite: avoid distributed tracing headers in direct/browser mode

Document table row merge for multiple queries

* everything imported via systemjs in the path `plugin/` will get a
 timestamp appended for cache busting
* timestamp is set once on page load
* plugin css loader gets cache buster too

docker: new block for elasticsearch6

[skip ci]

inviting users: show friendlier error message when smtp is not configured

Closes #12061

* 9703-auth-proxy:
  go fmt fixes
  configure proxy environments for Transport property

related issue: https://github.com/grafana/grafana/issues/9703

closes #11494

fixes #12087

* Add a full range option to sparklines

* line zero=false

Motivation:

* too many conditionals for config, better to be explicit
* different priorities: faster build for hot mode
* working SCSS sources for styles in hot mode

The biggest differences:

* removed linter from TS loader in hot (should be editor or precommit
 or responsibility)
* simplified styles loading
* hot needs more extensions to resolve
* removed commons chunking for hot
* removed devServer from dev

Reduced HMR time from 8s to 4s on my machine.

* upgrade all webpack loaders to recent version
* keep TS loader at 4.0.0 (5.0.0 requires webpack 4)
* remove unused json-loader

Resolves issue with postgres tests.
Also sets timezone of test instance and database to utc to resolve
mysql tests.
Closes #12065